The invention relates to a magnetic resonance apparatus for determining a spin resonance distribution from spin resonance signals which can be generated in a part of an object containing atomic spins, such as nuclear spins, said apparatus comprising means for generating a steady, uniform magnetic field, means for generating RF electromagnetic pulses, means for generating at least one magnetic field gradient which is superposed on the uniform magnetic field, a detection chain comprising a variable-gain amplifier for receiving, detecting and sampling the resonance signals, processing means which include programmed means for processing the sampled resonance signals, and control means which are suitable for controlling said means so that a pulse and gradient sequence is applied to the object a number of times in order to obtain the sampled resonance signals for image reconstruction, said pulse and gradient sequence comprising at least one RF excitation pulse for exciting the spins in the uniform field and a phase encoding gradient for encoding the phase of the spins, a value of a time integral over the phase encoding gradient varying over the applied pulse and gradient sequences.
A magnetic resonance apparatus this kind can be used, for example for forming MR tomograms of objects such as a (human) body. For example grey scale images can be made of proton concentrations in a slice of the object, but also spectroscopic images containing metabolic information can be made. In the case of spin resonance radio waves are used for the excitation of nuclear spins. The device could be used not only for nuclear spins but also for electron spins, be it that in the latter case additional harware as customarily used for electron spin resonance is required, for example an excitation and receiving device for microwaves.
A magnetic resonance apparatus of this kind is known from British Patent Application no. 2,177,861. The adjusting means for adjusting the gain in an apparatus of this kind are used to adapt the receiving chain to varying signal strength of echo resonance signals for different IMR images in the case of multiple echo sequences in order to obtain comparable images, which are to be reconstructed from samples associated with corresponding echo resonance signals. The gain within a data set is then constant. Even though at least for multiple echo sequences better use is made of the dynamic range of the receiving chain at least for multiple echo sequences, this is not the case in relation to resonance signals generated in order to obtain a data set for a IMR image.